Lingerd is a daemon (service) designed to take over the job of properly
closing network connections from an http server like Apache.
Because of some technical complications in the way TCP/IP and HTTP work,
each Apache process currently wastes a lot of time "lingering"
on client connections, after the page has been generated and sent.
Lingerd takes over this job, leaving the Apache process immediately free
to handle a new connection. As a result, Lingerd makes it possible to
serve the same load using considerably fewer Apache processes. This
translates into a reduced load on the server.
Lingerd is particularily useful in Apache webservers that generate
dynamic pages (e.g in conjunction with mod_perl, mod_php or Java/Jakarta/Tomcat).
More importantely, lingerd can only do an effective job if HTTP
Keep-Alives are turned off; since keep-alives are useful for images, the
recommended lingerd setup is to have an Apache/mod_whatever/lingerd
server for the dynamic pages, and a plain Apache (or thttpd or boa) for the images.